The present invention relates to a spindle motor used in flexible disk drives among other things.
One example of spindle motor structure according to the prior art is described in the U.S. Pat. No. 5,132,856. Referring to FIG. 25 here based on FIG. 1 of said Gazette, a rotor 91 is fitted to a shaft 96, and a magnet 92 is fitted to the rotor 91. The magnet 92 faces the tip of a stator core 93, which is fitted on a base plate 94. Around the stator core 93 is wound a coil 95. By supplying a current to the coil 95, a magnetic flux is generated at the tip of the stator core, and this magnetic flux gives the magnet 92 a magnetic force, which rotates the rotor 91.
In recent years, computers have been quickly reduced in size, and in this connection, floppy disk drives to be mounted on computers are also required to be reduced in size. Among the dimensions of floppy disk drives, the width and the length have been appreciably reduced, and accordingly, the development of a technology to make available thinner floppy disk drives is called for. In order to reduce the thickness T of the spindle motor shown in FIG. 25, either the stator core 93 or the coil 95 has to be made thinner.
However, thinning the stator core 93 would reduce the magnetic flux passing the poles of the stator core 93, because the stator core 93 would become magnetically saturated. The poles of the stator core 93 here refer to the radially extending parts of the stator core 93. A decrease in the magnetic flux passing the poles of the stator core 93 would reduce the torque of the spindle motor.
Or, if the diameter of the wire constituting the coil 95 is reduced to make the coil 95 thinner, its electric resistance will increase and thereby invite a decrease in the current passing the coil 95, which would in turn reduce the magnetic flux generated by the coil 95. A decrease in the magnetic flux generated by the coil 95 would invite a drop in the magnetic flux passing the stator core 93, and thereby the magnetic force given to the magnet 92 is reduced. This reduction of the magnetic force results in a decrease in the torque of the spindle motor.
As explained above, any technology to thin the spindle motor by reducing the thickness of the stator core 93 or of the coil 93 would entail a decrease in the torque of the spindle motor.